US3416537A - Tobacco sheet manufacture of high wet strength - Google Patents

Description

United States Patent ABSTRACT OF THE DISCLOSURE This invention relates to the manufacture of coherent tobacco products suitable for smoking and more particularly to such tobacco products in the form of a leaf or foil with an appearance and other physical qualities that they may be applied as the outer wrapper of cigars, cigarillos and the like in lieu of leaf tobacco ordinarily used as such wrapper. A feature of the new tobacco products is high resistance to disintegration when moistened and even chewed.

In essence, tobacco products of high wet strength are made of comminuted tobacco and film-forming cellulose derivatives which are substantially insoluble in water at normal (25 C.) and higher temperatures but are substantially soluble in organic acid of not less than about 15% by weight concentration in water. Preferably, the water-insoluble cellulose derivative is dissolved in formic or acetic acid of about 20% to 40% by weight concentration in water. While a tobacco sheet produced simply by admixing dry-ground tobacco powder with a solution of a cellulose derivative in acetic acid, casting and drying the resultant tobacco suspension will have high wet strength, such tobacco sheet will not have adequate resistance to chewing particularly when used as wrapper on large cigars that are frequently subjected to excessive chewing by some smokers. However, where chew resistance in addition to wet strength is desired in a tobacco sheet, this is achieved pursuant to the invention by incorporating in the suspension of tobacco in acetic acid highly hydrated, well-beaten cellulose fibers which may be derived from tobacco, particularly tobacco stems, or other plants as is known in the pulp art.

The particularly valuable tobacco sheets which include cellulose fibers for chew resistance have been made possible by the dual nature of the solvent used in accordance with this invention which combines organic acid to dissolve the water-insoluble cellulose derivative with Water to hydrate the cellulose fibers.

Background of invention There has long been a need for tobacco sheets of high wet strength and good chew resistance, particularly for use as wrappers on cigars. Numerous proposals have been made but none has been completely satisfactory.

Detert et al. first disclosed in US. Patent 2,893,400 a tobacco sheet for use as cigar wrapper made from finely pulverized tobacco and methylcellulose dissolved in an anhydrous solvent consisting of a mixture of methanol and methylene chloride. However, these patentees admitted the low wet strength of their tobacco sheet in US. Patent 2,927,588 wherein they proposed the addition of phosphoric acid to the mixture of finely pulverized tobacco and an anhydrous solution of methycellulose. The addition of phosphoric acid was alleged to have the surprising result that the resistance of the tobacco foils to tearing, their resistance to water, and their stability in storage are improved to such an extent that they can be manipulated without difiiculty either by hand or by machines. Interestingly enough, the patentees still did not allege that their tobacco sheet had any chew resistance and they failed to take into account that phosphoric acid is known to be a combustion retardant.

In still another effort to find a satisfactory process, Detert et a1. later suggested in US. Patent 3,062,688 that finely pulverized tobacco be mixed with a solution of a combination of water-soluble methylcellulose and a waterinsoluble cellulose derivative in an organic solvent consisting of a mixture of methylene chloride and methyl alcohol. The tobacco foil thus produced was alleged by the patentees to overcome the disadvantages of their prior foils which, in the words of the patentees, do not meet the high requirements of cover leaves for cigars and cigarillos with respect to their resistance to tearing and to saliva, and also because they have not sufficient suppleness. However, even this latest proposal of Detert et al. fails to produce a tobacco sheet of sufficiently high wet strength and chew resistance to be acceptable as wrapper on cigars that are subjected to wet-chewing by many smokers.

Another approach to the same problem has been the concept of producing tobacco sheets with water-soluble binding or film-forming agents together with cross-linking agents which are intended to render the resultant tobacco sheet water-insoluble. Thus, it was proposed in US. Patent 2,769,734 that a water-soluble binding agent be cross-linked by glyoxal. U.S. Patent 2,887,414 disclosed the use of dialdehyde starch as cross-linking agent for a water-soluble binding agent, while US. Patent 3,106,212 suggested the use of moisture resistance agents such as melamine formaldehydes and urea formaldehydes with water-soluble binding agents to produce moisture resistant tobacco sheets. These and other similar proposals have proved to be unsatisfactory for such reasons as poor smoking taste arising from the use of the cross-linking agents, darkening of the tobacco by the cross-linking agents, instability of the water resistance of the tobacco sheets during prolonged storage, and stiffening of the tobacco sheets to an extent that they fail to conform satisfactorily when applied as wrappers on shaped cigars.

Description of invention Fundamental to the invention is the selection of an aqueous solution of organic acid as the solvent for cellulose derivatives which are known to be binding agents or film-formers but which are substantially insoluble in water at normal (25 C.) or higher temperatures. The organic acid must be completely miscible with water and volatile at temperatures which may be used to dry the tobacco product without substantial impairment of its smoking quality. Formic and acetic acids best fulfill these requirements of the organic acid used as solvent. Acetic acid is preferred particularly inasmuch as it is less expensive than formic acid. While aqueous organic acid with as low as 15% by weight concentration and as high as concentration may serve as solvent, the preferred solvent is generally in the range of about 20% to 40% by weight of formic or acetic acid in Water.

The water-insoluble cellulose derivative chosen for the production of a tobacco sheet or other coherent form must be soluble at normal temperature in the aqueous organic acid used as solvent. Since the preferred solvent is aqueous formic or acetic acid in the range of about 20% to 40% by weight concentration, the preferred water-insoluble cellulose derivatives are those which are substantially soluble in such solvent even though water-insoluble cellulose derivatives requiring aqueous formic or acetic acid of as high as about 80% by weight concentration may be used pursuant to this invention. It is well to note that generally the dissolving of the water-insoluble cellulose derivative is preferably carried out by initially using an organic acid of higher concentration than is ultimately desired for the production of a tobacco sheet or other coherent form of tobacco, and then adding water to the solution to bring the concentration of the organic acid to the desired value. Many of the water-insoluble cellulose derivatives useful pursuant to this invention require this dissolving procedure because they are not adequately dissolved by direct suspension, say, in aqueous acetic acid of about 20% to 40% by weight concentration but they remain substantially in solution when their solutions in glacial acetic acid or in concentrated acetic acid, e.g., about 80% by weight concentration, are diluted with water to acetic acid solutions of about 20% to 40% by weight acid concentration.

The organic acid used as solvent pursuant to this invenion may be not only a mixture of formic and acetic acids but also a mixture of either or both of these acids with a somewhat less volatile acid like propionic acid or even a substantially non-volatile acid like lactic or citric acid. Poorly volatile and non-volatile acids are used as only the minor component in admixtures with formic or acetic acid. The use of a minor proportion of a non-volatile acid such as malic or tartaric acid as well as lactic or citric acid serves the dual purpose of acting as part of the organic acid solvent for the water-insoluble cellulose derivative and of plasticizing the tobacco product to render it more flexible and workable in making cigars especially when the product is a tobacco sheet applied as cigar wrapper. Generally, such acids that remain in a tobacco product made pursuant to this invention are used in an amount not exceeding about 20% by Weight based on the tobacco content of the product. Even at such a comparatively high level of acid in the tobacco product, hydroxylated polycarboxylic acids in particular have been found to be not objectionable during the smoking of the tobacco product.

Dry-ground or pulverized tobacco may be formed into a coherent form having appreciable wet strength with the aid of a water-insoluble cellulose derivative dissolved in aqueous formic or acetic acid. In such case where no fiber is present in formulating the tobacco product, the use of a minor amount of plasticizing acid such as citric or lactic as part of the aqueous organic acid is generally advisable inasmuch as the plasticizing acid tends to prevent cracking especially when the product is a tobacco sheet. However, considerably higher wet strength may be obtained by incorporating in the formed tobacco product highly hydrated, well-beaten cellulose fibers. The pulp of refined cellulose fibers may be prepared from tobacco, particularly stems, or from the usual sources used in the pulp industry. In terms of the improved physical properties, especially tensile strength, of a tobacco sheet achieved by incorporating a certain weight percentage of refined fibers of the sulfite or sulfate type pulp, generally at least twice as much refined fibers derived from tobacco stems are required for the same improved properties.

The selection of the water-insoluble cellulose derivative to be used as binding agent is based not only on its solubility in aqueous organic acid, especially acetic acid, but also on its viscosity when so dissolved. A water-soluble cellulose derivative like methylcellulose may be made Water-insoluble by increasing the degree of substitution of hydroxyl hydrogen in the original cellulose molecular chain with hydrophobic substituents like methyl, ethyl and acetyl. However, it is known that the cellulose molecular chain tends to degrade or break into shorter chains as the degree of substitution is increased. Since the binding or film-forming capacity of cellulose derivatives in tobacco sheets and other coherent bodies generally decreases as the cellulose molecular chains become shorter, it is important for the purposes of this invention to select cellulose derivatives in which the degree of substitution has been increased just enough to make the cellulose derivative substantially water-insoluble without degrading the molecular chains to an extent that the binding capacity of the cellulose derivative has been seriously impaired.

The length of cellulose molecular chains, commonly referred to as degree of polymerization, is frequently determined by the viscosity of the cellulose derivative in a given solvent, at a given concentration and at a given temperature. Thus, the degree of polymerization or viscosity grade of a water-soluble cellulose derivative like methylcellulose is usually established by the viscosity in centipoises (cps) at a temperature of C. for a water solution containing 2% by weight of the cellulose derivative. For the Water-insoluble cellulose derivatives used in accordance with this invention, it has been found desirable to determine the degree of polymerization, hereinafter called the acid viscosity grade, by measuring in a Brookfieid R.V.T. viscosimeter (speed 20 revolutions per minute) the viscosity at a temperature of C. of 1% by Weight of the cellulose derivative dissolved in aqueous acetic acid having an acetic acid content of 80% by weight. Generally, the water-insoluble cellulose derivative used pursuant to this invention is desirably one having an acid viscosity grade of at least about 100 cps. and preferably at least about 250 cps.

Water-insoluble cellulose derivatives suitable for the purposes of this invention include water-insoluble grades of methylcellulose, ethylmethylcellulose, ethylcellulose,

ethylhydroxyethylcellulose and cellulose acetate. Another group of suitable binding agents comprises water-soluble grades of cellulose derivatives such as methylcellulose, hydroxyethylcellulose, methylhydroxyethylcellulose, ethylhydroxyethylcellulose, methylhydroxypropylcellulose and methylhydroxybutylcellulose which have been acetylated to the extent of rendering the cellulose derivatives substantially insoluble in water at normal and higher temperatures. For example, water-soluble methylcellulose of 8000 cps. viscosity grade (2% by weight in water at a temperature of 20 C.) and having a methoxyl content of about by weight that has been acetylated to the extent that the cellulose derivative has an acetyl content of between about 5% and 12% by weight has been found to be substantially water-insoluble but soluble in aqueous acetic acid of about 20% to by weight concentration.

It should be noted that the water-insoluble cellulose derivatives useful for the purposes of this invention embrace not only the commercially available types that are soluble in the conventional organic solvents such as a mixture of methylene chloride and methanol but also specially prepared types that are generally considered unsatisfactory for solution in such conventional organic solvents. For instance, commercially available ethylcellulose has an ethoxyl content of over about 44% by weight and cellulose acetate has an acetyl content of over about 37% by weight; such cellulose derivatives are soluble in aqueous formic or acetic acid of about by weight concentration. On the other hand, ethylcellulose and cellulose acetate made with, respectively, lower ethoxyl and acetyl contents (but not low enough to make these cellulose derivatives substantially soluble in water) are soluble in less concentrated aqueous formic or acetic acid with an acid content going down to about 15% by weight.

The specially made cellulose derivatives in contrast to the types which are commercially produced for solution in conventional organic solvents offer the advantages of obviating the use both of such highly concentrated organic acid as aqueous acetic acid of 80% by weight concentration and of the comparatively larger proportion of highly hydrated, refined cellulose fibers required to prevent cracking of a tobacco sheet during its manufacture with a cellulose derivative of the type offered commercially for solution in conventional organic solvents. Moreover, a tobacco sheet made with the latter type of cellulose derivative is usually not sufficiently plasticized by water to make it stretchable enough for use as wrapper on cigars of the perfecto or like shapes; in such case, a watersoluble or highly water-susceptible binding agent is desirably used together with the cellulose derivative so that the resulting tobacco sheet can be plasticized by water to give it the desired degree of stretch or elasticity.

While humectants and plasticizers such as glycerol, sorbitol and various glycols are generally used in tobacco smoking products to avoid excessive drying and embrittlement, it is noteworthy that tobacco sheets and other coherent bodies of tobacco produced in accordance with this invention rarely require the use of humectants or plasticizers because water alone is an adequate plasticizer. It has been known that tobacco sheets with a high moisture content, usually over by weight, are during prolonged storage susceptible to deterioration in one form or another such as loss of strength, change of appearance or even mold formation. By contrast, the tobacco sheets of this invention may be made with a comparatively low moisture content, say about 20% by weight, so as to have good stability during prolonged storage. While such tobacco sheets will have poor elasticity, this physical limitation is easily corrected at the time such tobacco sheets are being utilized in the manufacture of a smoking product, such as wrapper on cigars, by moistening with water. The tobacco sheets of the invention may be moistened by a water spray, by contacting a wet roller or even by dipping. The moistening of the tobacco sheets with water is desirably controlled so that the moisture content then generally is in the range of about to by Weight inasmuch as such moistened tobacco sheets have the necessary stretch and other physical properties to be successfully applied as wrappers on cigars of even intricate shapes. Obviously, the amount of water added to a tobacco sheet need not be more than that just required to make the workability of the tobacco sheet satisfactory for its intended use such as wrapper on cigars.

When a tobacco sheet is to be applied as the outer covering or wrapper of a cigar, the addition of an ashwhitening material like titanium dioxide and an ashstrengthening agent like comminuted ceramic fiber to the basic components of the tobacco sheet may be advisable.

The coherent tobacco products of this invention may be used in cigarettes, pipe tobaccos and like smoking products but the high wet strength and chew resistance that may be achieved in tobacco sheets made by this invention clearly indicate that such tobacco sheets are especially attractive for use as wrappers on cigars. Hence, further elaboration of the invention will be made in terms of its most valuable commercial application, namely, tobacco sheets used as wrappers on cigars.

For a better understanding of the invention and its scope, illustrative embodiments are presented hereinbelow in detail. In the examples, proportions are given in parts and percentages by weight unless otherwise specified.

EXAMPLE 1 Burley tobacco stems cut to pieces of about 1 inch in length were admixed with water to form a 7.4% suspension which was placed in .a sealed autoclave for treatment in accordance with the process of US. Patent 3,076,729 to Garbo. Approximately 25% of the volumetric capacity of the autoclave was charged with commercially pure oxygen at an initial pressure of 700 p.s.i.g. (pounds per square inch gauge). While stirring, the stem suspension was heated until a temperature of about 300 F. was reached and then this temperature was maintained for a 20-minute period during which the pressure was held at about 1200 p.s.i.g. and with the help of added oxygen when needed. Thereupon, the suspension in the autoclave was rapidly cooled to a temperature of about 175 F. and discharged at .a pressure of about p.s.i.g. through a Rietz disintegrator fitted with a screen having /o, -inch openings.

The thus treated suspension was filtered to discard the liquid and the residual stern material was so washed on the filter that the dry solids of the washed stem material had a ratio of total solids to water-insoluble solids, hereinafter called the wash ratio, of 1.2. The washed stem material was again dispersed in water to form a 6% suspension based on the dry solids of the washed stem material and this suspension with added titanium dioxide was repeatedly passed through a disc refiner until the refined stern fiber had a reverse freeness of 70 as determined by the Schopper-Riegler type beating and freeness tester. The titanium dioxide which was added to the stem suspension in the ratio of 1 part to 12.5 parts of dry solids in the suspension served two purposes, namely, lightening the color of the finished tobacco sheet and yielding a whitish ash when the tobacco sheet was smoked as wrapper on a cigar.

The refined pulp of Burley stems was admixed with water-insoluble methylcellulose (39.5% methoxyl content) having an acid viscosity grade of 310 c.p.s. that had been dissolved in aqueous acetic acid .and was further admixed with a dry-ground blend of cigar-type tobaccos based principally on Wisconsin tobacco. The pulverized tobacco blend passed through -mesh screen (U.S. Sieve size) but only 85% passed through ZOO-mesh screen. To strengthen the ash of the tobacco sheet, a ceramic fiber (Fiberfrax sold by The Carborundum Company), which was cut to very short fragments while suspended in water by a high-speed, high-shear stirrer, was also added to the pulp of Burley stems. The proportioning of the admixed components was such that the final slurry contained:

Parts Pulverized tobacco blend 150 Refined Burley stems (dry solids) Water-insoluble methylcellulose 40 Titanium dioxide 10 Ceramic fiber 3 all in 20% aqueous acetic acid at a total concentration of 5.9% of the aqueous acetic acid. The final slurry had a viscosity of 7000 cps. at a temperature of 10 C.

This slurry was spread evenly on a stainless steel belt which was subsequently heated first with hot air impingement on the slurry-coated belt and as soon as enough water and acetic acid had been removed by evaporation to set the slurry coating on the belt was further heated with steam condensation on the underside of the steel belt. The dried coating on the belt was rehumi'dified to a moisture content of about 35% and stripped from the belt as a tobacco sheet. The moisture content was decreased to about 20% with the aid of infra-red lamps and the tobacco sheet approximately 0.002 inch thick was then wound up in rolls suitable for use on a cigarmaking machine.

The tobacco sheet had a pleasing appearance and a brown color similar to that of some grades of cigar wrapper leaf tobacco. The Finch tensile strength of this tobacco sheet, determined according to ASTM standard test D829-48, using an immersion time of 30 seeonds in water and a test sample of double width, was 125 g./mm. (grams per square millimeter).

Perfecto-shape cigar bunches were wrapped with this tobacco sheet after increasing its moisture content to about 45 since at this high moisture content the tobacco sheet had good stretch so that it could be pulled over the curved portions of the perfecto-shape cigar bunches and thus confonm to the shape without forming gaps of creases in the Wrapper sheet. At the time of application of the tobacco sheet as cigar wrapper, an odor of acetic acid was noticed because of the volatilization of a small residue of acetic acid in the tobacco sheet as stripped from the stainless steel belt. However, after the finished cigars were dried to an average moisture content of about 13%, the odor of acetic acid had vanished.

The perfecto-shaipe cigars with the tobacco sheet wrapper were found to burn with an attractive whitish, firm ash and to have a very agreeable smoke taste. Smokers who are accustomed to dhewing a cigar while smoking it noted that this tobacco sheet Wrapper withstood chewing better than most tobacco leaf wrappers.

7 EXAMPLE 2 Burley tobacco stems processed as in Example 1 but refined to a reverse freeness of 92 were passed from the disc refiner once through a valve-type homogenizer at a pressure of 4500 p.s.i.g. Only 1 part of titanium dioxide was added to 100 parts of dry solids in the tobacco stem suspension prior to refining this suspension.

Ethylcellulose of 35.5% ethoxyl content was dissolved in aqueous acetic acid of 70% by weight concentration and was admixed with a dry-ground blend of 50% Sumatra and 50% Santo Domingo tobaccos, all passing through 100-mesh screen. The components were admixed to give a final slurry containing:

Parts Pulverized tobacco blend 150 Refined Burley stems (dry solids) 100 Ethylcellulose 50 Titanium dioxide 1 all in 45% aqueous acetic acid at a total concentration of 6% of the aqueous acetic acid.

This slurry was converted into a tobacco sheet as described in Example 1. The appearance and physical properties of this tobacco sheet were comparable to those of the tobacco sheet of Example 1.

Blunt-shape cigars were made with the tobacco sheet of this example as wrapper. The cigars had the typical appearance of moderate-priced cigars and, in smoking tests, were found to have considerable chew-resistance and a pleasing smoke taste.

EXAMPLE 3 The Burley stems of Example 1 were first passed through heated rolls moving a difierential speeds which flattened and tore the stem pieces to yield a product in chip form, called flaked stems. The flaked stems were suspended in water, autoclaved and further processed including washing to a wash ratio of 1.1 as described in Example 1. The washed stern material with the added titanium dioxide was. refined and homogenized as described in Example 2.

The thus prepared Burley stems were dewatered to a solids content of 15% and added slowly with high agitation to a solution of a mixture of 37.5 parts of methylcellulose (39% methoxyl content) and 12.5 parts of ethylcellulose (45% ethoxyl content) in glacial acetic acid until 100 parts (dry solids basis) of the stem material had been added. Water was then added slowly under high agitation to bring the acetic acid concentration to 80%. Finally, 100 parts of a blend of dry-ground Wisconsin tobacco and tobacco fines from cigar manufacture were added. The resulting slurry, having a solids content of 4.5% and a viscosity of 21,000 cps. at 20 C., was formed into a tobacco sheet as described in Example 1. The product was light in color, resembling a desirable cigar wrapper, and had properties suitable for conformance to shaped cigars.

EXAMPLE 4 The procedure in Example 3 was followed in all details except that in place of 37.5 parts of the waterinsoluble methylcellulose, 25 parts of water-soluble methylcellulose (30% methoxyl content) of 1500 cps. viscosity grade was used, while the quantity of the ethylcellulose was doubled to 25 parts. The resulting tobacco sheet in appearance, physical properties and smoking qualities was very satisfactory as a cigar wrapper.

EXAMPLE 5 Flaked Burley stems were processed as in Example 3 except that a conical refiner was used instead of the disc refiner. To a solution of 50 parts of ethylmethylcellulose with a degree of substitution of 0.94 ethyl and 1.34 methyl (acid viscosity grade of 110 cps.) in glacial acetic acid were added 100 parts (dry solids basis) of the refined and homogenized Burley stem material. Sufiicient water was added to bring the acetic acid concentration to 30% and then 150 parts of dry-ground Sumatra tobacco were admixed to yield a slurry containing 7.5% solids. After deaeration, the slurry had a viscosity of 12,800 cps. at a temperature of 11 C.

The slurry was converted to a tobacco sheet as described in Example 1. The resulting tobacco sheet had good cigar wrapper properties including attractive color and texture. Panatella-shape cigars made with this wrapper sheet withstood considerable chewing during smoking tests in which the smoke taste was rated very good.

EXAMPLE 6 The processed Burley stems of Example 3 were added to the extent of 50 parts (dry solids basis) to a solution of 20 parts of acetylated methylcellulose (prepared by acetylating water-soluble methylcellulose of 8000 cps. viscosity grade to 8% acetyl content) in glacial acetic acid. Sufiicient water was added to bring the acetic acid concentration to 35% and then 150 parts of dry-ground Java tobacco were admixed to yield a slurry with a solids content of 7% and a viscosity of 6500 cps. at 30 C.

The tobacco sheet formed from this slurry as described in Example 1, having an unusually high tobacco content (91% dry basis), had a tensile strength of 495 g./mm'. and a Finch tensile strength of g./mrn. Its performance as a cigar wrapper was very satisfactory.

EXAMPLE 7 Cellulose fibers (fully bleached sulfate softwood pulp) were dispersed in water at a dry solids concentration of 3% and passed repeatedly through a disc refiner until a Schopper-Riegler reverse freeness of 470 was attained. Eighty parts of acetylated methylcellulose (8.4% acetyl content, 28% methoxyl content, acid viscosity grade of 920 cps.) were dissolved in 4940 parts of 70% aqueous acetic acid. Twenty parts of water-soluble methylcellulose (8000 cps. viscosity grade) were dissolved in the same acetic acid solution.

The refined cellulose fiber slurry was added to the extent of parts (dry solids basis) to the aqueous acetic acid solution of the cellulose derivatives under high agitation. Then 15 parts of titanium dioxide, 5 parts of fragmented Fiberfrax and 800 parts of Connecticut shade wrapper tobacco cuttings, which had been dry-ground so that 100% passed through 100-mesh screen and passed through ZOO-mesh screen, were uniformly dispersed in the cellulose fiber slurry. The entire mixture was diluted with 3690 parts of water to bring the acetic acid concentration to 30%. The viscosity of the final mixture was 6600 cps. at a temperature of 21 C.

The tobacco sheet produced from this final mixture as described in Example 1 was found to be adequate in all respects as a cigar wrapper.

EXAMPLE 8 Flaked Connecticut shade tobacco stems were suspended in water at a concentration of 7.5 autoclaved, filtered, washed and refined as described in Example 1. A 4% solution in 50% aqueous formic acid was prepared of a mixture of acetylated methylcellulose (8.4% acetyl content, 28% methoxyl content, acid viscosity grade of 360 cps.) and water-insoluble methylcellulose having 40.3% methoxyl content (acid viscosity grade of 345 cps).

A slurry of refined cellulose fibers was prepared as described in Example 7. The processed Connecticut shade tobacco stem slurry and the refined cellulose fiber slurry were mixed together and added to the aqueous formic acid solution of the cellulose derivatives. To this mixed slurry, dry-ground Connecticut shade wrapper tobacco cuttings as described in Example 7, Fiberfrax, and titanium dioxide were added. The final slurry had 7% solids in aqueous formic acid of 40% concentration and contained:

Parts Processed Connecticut shade tobacco stems (dry solids) 20.0 Refined cellulose fibers (dry solids) 10.0 Ground Connecticut shade wrapper tobacco 55.0 Acetylated methylcellulose 3.0 Water-insoluble methylcellulose 9.5 Fiberfrax 0.75 Titanium dioxide 1.75

The final slurry was converted into a tobacco sheet having a dry weight of 35 g./rnm. (grams per square meter), a tensile strength of 870 g./mm. and a Finch tensile strength of 170 g./mm. Used as a cigar wrapper, the product had high chew resistance and pleasing smoking qualities.

EXAMPLE 9 To 1358 parts of a 6'% solution of cellulose acetate (about 28% acetyl content) in aqueous acetic acid of about 40% acid content were added 2260 parts of glacial acetic acid. To this solution were added 1250 parts of a 3.6% aqueous solution of water-soluble methylcellulose (30% methoxyl content) of 1500 cps. viscosity grade, 35 parts of a 50% aqueous slurry of titanium dioxide, 7.5 parts of fragmented Fiberfrax, and 1462 parts of water. Then 4000 parts of the aqueous slurry of refined cellulose fibers prepared as described in Example 7 but diluted to a dry solids concentration of 2.5% were added. Finally, 750 parts of a dry-ground mixture of Wisconsin tobacco and tobacco fines resulting from cigar manufacture were thoroughly blended into the total slurry which was diluted with 2000 parts of water to adjust the acetic acid concentration to 30% and the viscosity to 5500 cps. at a temperature of 21 C.

The tobacco sheet made from this final slurry as described in Example 1 had a dry weight of 37 g./m. and a Finch tensile strength of 190 g./mm. This product had the desirable characteristics of good cigar wrapper tobacco.

EXAMPLE 10 To 75 parts of acetylated hydroxyethylcellulose (degree of substitution of 1.5 acetyl, molecular substitution of 1.1 hydroxyethyl) slurried in 750 parts of water were added under agitation 1890 parts of glacial acetic acid. To the resulting solution were added 1000 parts of water, 4.5 parts of fragmented Fiberfrax, and 21 parts of a 50% aqueous slurry of titanium dioxide. Next, 1720 parts of the aqueous slurry of refined cellulose fibers prepared as described in Example 7 but concentrated to a dry solids content of 3.5% and 450 parts of dry-ground Connecticut shape wrapper tobacco as described in Example 7 were blended with the solution of cellulose derivative. The total slurry was diluted with 990 parts of water so that the final acetic acid concentration was 30% and the viscosity of the slurry was 7000 cps. at C.

The tobacco sheet made from this slurry as described in Example 1 was attractive in appearance and served as a cigar wrapper of good smoke taste and chew resistance.

EXAMPLE 11 A mixture of 3 parts of acetylated methylcellulose (9.3% acetyl content, 28% methoxyl content) and 9.5 parts of water-insoluble methylcellulose (39.5% methoxyl content) was suspended in 60 parts of water and under high agitation 303 parts of glacial acetic acid were added. To the resulting solution were added 10 parts (dry solids basis) of autoclaved, filtered, washed, and refined Connecticut shade tobacco stems as described in Example 1 and 55 parts of Connecticut shade wrapper tobacco ground so that 100% passed through IOO-mesh screen and 60% passed through ZOO-mesh screen together with 20 parts of Connecticut shade tobacco stems ground so that 100% passed through -mesh screen and passed through ZOO-mesh screen. To this mixture were added 1.75 parts of titanium dioxide and 0.75 part of comminuted Fiberfrax. Sufiicient water was added to the total mixture to bring the acetic acid concentration to 30%, the solids content to 9% and the viscosity to 11,400 cps. at a temperature of 75 C.

The tobacco sheet made from the final mixture had a pleasing color, conformed well to shaped cigars and was as chew resistant as wrapped tobacco of good quality.

EXAMPLE 12 Flaked Burley stems were cooked as a 12.5% suspension in water in a heated kettle with stirring for one hour at a temperature of 120 F. This suspension was then passed through a Rietz disintegrator fitted with a screen having -inch openings, filtered and washed to a wash ratio of 1.2. The fibrous stem mass was redispersed in water to give a 5% suspension which was refined by 29 passes through a disc refiner and then one pass through a valve-type homogenizer at a pressure of 4500 p.s.i.g.

The thus processed Burley stems were slowly added under high agitation to a solution of 40 parts of waterinsoluble methylcellulose (39.5% methoxyl content) in 1630 parts of 80% aqueous acetic acid until 150 parts (dry solids basis) of the processed stems were incorporated. Then 150 parts of dry-ground Pennsylvania tobacco stems passed through ZOO-mesh screen) and 3 parts of fragmented Fiberfrax were added under high agitation. The mixture was slowly diluted under high agitation with water to reduce the acetic acid concentration to 30%. The final slurry had a solids content of 6.8% and a viscosity of 16,000 cps. at 11 C.

Tobacco sheet produced from the final slurry as described in Example 1 had a good light-brown color and performed satisfactorily in all respects as a cigar wrapper.

EXAMPLE 13 Flaked Connecticut shade tobacco stems were processed as described in Example 8. The resulting stem slurry was cooled to a temperature of 50 F. and added slowly with high agitation to a solution of 3 parts of acetylated methylcellulose (5% acetyl content, 29% methoxyl content, acid viscosity grade of 560 cps.) in 400 parts of glacial acetic acid until 97 parts (dry solids basis) of refined stem fibers were admixed.

The final slurry in aqueous acetic acid of 25% acid content was cast as a thin coating on a stainless steel belt with a doctor blade and the coating was evaporated to dryness as the belt traveled over steam pan dryers. The resulting dry tobacco sheet was rehumidified, stripped from the belt and rolled up as described in Example 1.

This tobacco sheet contained, on a dry basis, only 3% of cellulose derivative but had physical properties adequate for its use as a chew-resistant cigar wrapper.

EXAMPLE 14 Seventy-five parts of dry-ground Connecticut shade wrapper tobacco cuttings (100% passed through 100- mesh screen and 85% passed through ZOO-mesh screen) were dispersed in 900 parts of a solution containing 25 parts of acetylated hydroxyethylcellulose (degree of substitution of 1.5 acetyl, molecular substitution of 1.1 hydroxyethyl) in aqueous acetic acid of 40% acid content.

Tobacco sheet with a dry weight of 40 g./m. was produced from the resulting slurry as described in Example 1. This tobacco sheet had a Finch tensile strength of about g./mm. and good elasticity at a moisture content of 40%; it was a very acceptable wrapper on panatella-shape cigars.

EXAMPLE 15 Seventy-five parts of the tobacco powder described in Example 14 were dispersed in 900 parts of a solution containing 25 parts of acetylated methylcellulose (10.1%

acetyl content, 28% methoxyl content, acid viscosity grade of 70 cps.) in a mixture of methylene chloride and methanol in which the weight ratio of the two solvents was 9: 1, respectively.

Tobacco sheet with a dry weight of 50 g./m. was produced from the resulting slurry and had a tensile strength of 475 g./mn1. and a Finch tensile strength of 130 g./ mm. As a cigar wrapper, this tobacco sheet was very similar to the product of Example 14.

Example 15 illustrates the aspect of the invention of using a water-insoluble acetylated cellulose derivative which was water-soluble prior to being acetylated. Tobacco sheets of high resistance to disintegration when moistened can be produced with such water-insoluble acetylated cellulose derivatives whether dissolved in aqueous organic acid as shown in Example 14 or dissolved in organic solvent as shown in Example 15. Other organic solvents suitable for water-insoluble acetylated cellulose derivatives disclosed hereinbefore as being effective and desirable binding agents for the production of tobacco sheets include such solvent mixtures, preferably in the indicated weight proportions, as 9 ethylene chloride-1 ethanol, 4 benzene-1 methanol, and acetone-1 ethanol.

The foregoing examples are illustrative of the many possible variations and modifications of the invention. The examples further show that the tobacco sheets of this invention can be utilized to satisfy the difficult and exacting requirements of good cigar wrapper. Such tobacco sheet can be made predominantly of comminuted tobacco which wholly or in part has been ground in essentially a dry form or in the form of a liquid suspension. The tobacco content of such tobacco sheets is generally not less than 75% by weight on a dry basis and frequently exceeds about 80%. The non-tobacco added components of these tobacco sheets, principally the cellulose derivative used as the binding agent and, in some cases, cellulosic fiber derived from plants other than tobacco such as softwood pulp, are present in minor proportions usually not exceeding 25% by weight of the dry tobacco sheet and frequently less than about 20%. The substantially water-insoluble methylcellulose found to be effective in producing a cigar wrapper type of tobacco sheet is one having a methoxyl content of at least about 38% by weight. As also demonstrated by the examples, ash-improving components such as titanium dioxide and finely divided ceramic fiber are effective when present to the extent of only a few percent, generally less than 3%, of the weight of the dry tobacco sheet.

What is claimed is:

1. The process of manufacturing a coherent tobacco product with appreciable wet strength and adapted for smoking, which comprises combining comminuted tobacco with a minor weight proportion, based on said tobacco, of a water-insoluble cellulose derivative dissolved in aqueous organic acid of not less than about by weight of organic acid content, the said organic acid having not more than two carbon atoms per molecule and converting the combined tobacco and solution of said cellulose derivative with drying into said coherent tobacco product.

2. The process of claim 1 wherein the aqueous organic acid is aqueous acetic acid of not less than about by weight of acetic acid content.

3. The process of claim 1 wherein a highly hydrated refined pulp of cellulosic fibers is combined with the comminuted tobacco and water-insoluble cellulose derivative dissolved in aqueous organic acid.

4. The process of claim 3 wherein the aqueous organic acid is aqueous acetic acid of not less than about 20% by weight of acetic acid content.

5. The process of claim 4 wherein the highly hydrated refined pulp of cellulosic fibers is at least in part derived from tobacco stems.

6. The process of claim 1 wherein the water-insoluble cellulose derivative is an acetylated form of an originally water-soluble cellulose derivative.

7. The process of claim 6 wherein a highly hydrated refined pulp of cellulosic fibers is combined with the comminuted tobacco and the acetylated cellulose derivative is dissolved in aqueous acetic acid of not less than about 20% by weight of acetic acid content.

8. The process of claim 1 wherein the water-insoluble cellulose derivative is methylcellulose with a methoxyl content of at least 38% by weight.

9. The process of claim 8 wherein a highly hydrated refined pulp of cellulosic fibers is combined with the comminuted tobacco and the methylcellulose is dissolved in aqueous acetic acid of not less than about 20% by weight of acetic acid content.

10. The process of manufacturing a tobacco sheet with appreciable chew-resistance and adapted for smoking, which comprises preparing an aqueous suspension of highly hydrated refined cellulosic fibers, dissolving a waterinsoluble cellulose derivative in organic acid of not more than two carbon atoms per molecule, mixing said aqueous suspension of fibers, the organic acid solution of said cellulose derivative and dry-ground tobacco so as to yield a slurry containing a minor weight proportion, based on said tobacco, of said cellulose derivative with the resulting aqueous organic acid having a content of not less than 20% by weight of said organic acid, casting said slurry as a thin layer, and drying said layer to produce said tobacco sheet.

11. The process of claim 10 wherein the organic acid is acetic acid.

12. The process of claim 11 wherein the water-insolu ble cellulose derivative is an acetylated form of an originally water-soluble cellulose derivative.

13. The process of claim 12 wherein the cellulosic fibers are derived predominantly from tobacco stems.

14. The process of claim 11 wherein the water-insoluble cellulose derivative is predominantly methylcellulose wtih a methoxyl content of at least 38% by weight and a minor addition of acetylated methylcellulose.

15. The process of claim 11 wherein the water-insoluble cellulose derivative is predominantly methylcellulose with a methoxyl content of at least 38% by weight and a minor addition of ethylcellulose.

16. The process of claim 11 wherein the water-insoluble cellulose derivative is predominantly methylcellulose with a methoxyl content of at least 38% by weight and a minor addition of acetylated hydroxyethylcellulose.

References Cited UNITED STATES PATENTS 2,576,021 11/1951 Koree 13l2 3,062,688 11/1962 Detert et al. 131-140 X 3,162,200 12/1964 Jansson et a1 131140 X 3,310,058 3/1967 Savage et al 13115 X 3,322,130 5/1967 Panzer et al. 13117 3,310,057 3/1967 Savage et al. 13115 w MELVIN D. REIN, Primary Examiner.

US. Cl. X.R.